Very strange. I first used a 7.4v on the ESC. It bee[pd very quietly. Motor never got good speed. I then plugged in an 11.1v to the ESC. Loud beeps motor got to high speed. Then after a while tried 7.4v again and now loud beeps and motor got a lot faster but still not fast enough. Wierd. Now either 11.1v or 7.4v gives loud beeps!!